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Abstract:

Disclosed are an optical element, an optical element array, and a method
of manufacturing an optical element capable of forming a desired
interface shape. In a microlens and a microlens array, at least one of a
transparent liquid forming a liquid phase and microbubbles forming a gas
phase is subjected to temperature adjustment by a curvature control part.
The transparent liquid and the microbubbles subjected to temperature
adjustment thermally expands or contracts, such that the shape of a
curved interface formed between the transparent liquid and the
microbubbles is changed.

Claims:

1-9. (canceled)

10. An optical element comprising: a container which transmits light; a
first transparent material which is accommodated in the container to form
a liquid phase; a second transparent material which is accommodated in
the container and generated by boiling of the first transparent material
to form a gas phase, a curved interface inflated toward the first
transparent material being formed between the first transparent material
and the second transparent material; and interface shape controller that
carries out temperature adjustment on at least one of the first
transparent material and the second transparent material to control the
shape of the interface.

11. The optical element according to claim 10, wherein the interface
shape controller thermally expands or contracts at least one of the first
transparent material and the second transparent material to control the
shape of the interface.

12. The optical element according to claim 10, wherein the interface
shape controller controls the curvature of the interface.

13. The optical element according to claim 10, wherein the interface
shape controller has a plate-shaped heat-generating portion formed at the
bottom of the container to generate heat through electrical connection,
and the heat-generating portion has a small-width portion at the center
thereof.

14. The optical element according to claim 10, wherein the container has
a first wall portion and a second wall portion arranged to face each
other, and the second transparent material is arranged separately around
the first wall portion and the second wall portion.

15. The optical element according to claim 10, wherein two containers are
provided, each container has a first wall portion and a second wall
portion arranged to face each other, in each container, the second
transparent material is arranged around the first wall portion, and the
first wall portions of the two containers are bonded to each other.

16. An optical element array in which a plurality of optical elements
according to claim 10 are arranged.

17. A method of manufacturing an optical element in which a conductive
liquid is filled in a container transmitting light, the method
comprising: an electrode forming step of using a container having one
opened surface, forming a first electrode at a position of the one
surface, and forming a second electrode at a position of another surface
facing the one surface; a liquid inflow step of charging a liquid,
applying a voltage having reverse charge to the liquid to the first
electrode, and allowing the liquid to flow into the container from the
one surface; and a liquid filling step of applying a voltage having the
same charge as the liquid to the first electrode, applying a voltage
having reverse charge to the liquid to the second electrode, and filling
the liquid in the container.

Description:

TECHNICAL FIELD

[0001] The present invention relates to an optical element, an optical
element array, and a method of manufacturing an optical element.

BACKGROUND ART

[0002] In the related art, as described in Japanese Unexamined Patent
Application Publication No. 2008-298821, as an optical element, a
diffraction grating is known through which light passes to control the
diffraction angle of light. The diffraction grating includes partition
walls arranged in parallel at regular intervals. An insulating liquid and
a conductive liquid are filled between adjacent partition walls. A
voltage is applied to the conductive liquid to change the position of the
interface formed between the liquids, such that the grating constant is
made variable.

[0003] The diffraction grating uses an electrowetting phenomenon
(electrocapilliary phenomenon). The electrowetting phenomenon is the
phenomenon that, when a voltage is applied to the conductive liquid and
the electrode, the surface tension of the liquid is changed and the shape
of the liquid surface is thus changed. With the use of this phenomenon,
in the diffraction grating, the voltage to be applied increases to lower
the surface tension of the liquid and to raise the position of the
interface.

[0005] However, in the above-described diffraction grating, the voltage is
applied to the liquid to change the shape or position of the interface,
making it difficult to change the interface in a desired shape or to a
desired position.

[0006] Accordingly, the invention has been finalized in order to solve the
technical problem, and an object of the invention is to provide an
optical element, an optical element array, and a method of manufacturing
an optical element capable of forming a desired interface shape.

Solution to Problem

[0007] That is, the invention provides an optical element. The optical
element includes a container which transmits light, a first transparent
material which is accommodated in the container to form a first phase, a
second transparent material which is accommodated in the container to
form a second phase different from the first phase, a curved interface
rounded toward the first transparent material being formed between the
first transparent material and the second transparent material, and
interface shape control means for carrying out temperature adjustment on
at least one of the first transparent material and the second transparent
material to control the shape of the interface.

[0008] According to the invention, the interface shape control means
carries out temperature adjustment on at least one of the first
transparent material forming the first phase and the second transparent
material forming the second phase. The transparent material subjected to
temperature adjustment thermally expands or contracts, such that the
shape of the curved interface formed between the first transparent
material and the second transparent material is changed. Thus, it becomes
possible to control the interface shape, thereby forming a desired
interface shape. Here, when a current is applied for temperature
adjustment, it is possible to reduce a voltage to be applied compared to
a case where a voltage is directly applied to the material in the
container to change the surface tension of the material. Therefore, if a
method which uses Joule heat based on a current is used, it is possible
to reduce a voltage to be applied and also to form a desired interface
shape.

[0009] It is preferable that the first phase is a liquid phase, and the
second phase is a gas phase.

[0010] According to the invention, the second transparent material forming
the gas phase is hardly influenced by gravity because of a small mass per
volume (low density). Therefore, it is possible to control the shape of
the interface accurately. It is also possible to prevent deterioration in
quality due to mixture compared to a liquid-liquid system.

[0011] It is preferable that the interface shape control means thermally
expands or contracts at least one of the first transparent material and
the second transparent material to control the shape of the interface.

[0012] According to the invention, the interface shape control means
thermally expands or contracts at least one of the first transparent
material and the second transparent material, making it easy to change
the shape of the interface. Therefore, it becomes possible to control the
interface shape.

[0013] It is preferable that the interface shape control means controls
the curvature of the interface.

[0014] According to the invention, since the interface shape control means
controls the curvature of the interface, it is possible to control
refractive power (lens power) when light passes through the container.

[0015] It is preferable that the interface shape control means has a
plate-shaped heat-generating portion formed at the bottom of the
container to generate heat through electrical connection, and the
heat-generating portion has a small-width portion at the center thereof.

[0016] According to the invention, since electrical resistance increases
in the small-width portion at the center of the heat-generating portion,
the temperature of the small-width portion is at the highest in the
heat-generating portion. Thus, it is possible to sufficiently heat the
transparent material near the center of the heat-generating portion with
a small current. Therefore, it is possible to easily thermally expand the
transparent material and to easily change the phase of the transparent
material, making it easy to control the shape of the transparent
material.

[0017] It is preferable that the container has a first wall portion and a
second wall portion arranged to face each other, and the second
transparent material is arranged separately around the first wall portion
and the second wall portion.

[0018] According to the invention, the first transparent material is
arranged so as to be sandwiched from both sides thereof by the second
transparent material between the first wall portion and the second wall
portion. Here, the shape of the interface formed between the first
transparent material and the second transparent material becomes a curved
shape rounded from the second transparent material toward the first
transparent material. For this reason, an interface is formed which has
two faces respectively rounded from the first wall portion and the second
wall portion inside the container. Therefore, a concave lens can be
formed between the first wall portion and the second wall portion by the
two-face interface.

[0019] It is preferable that two containers are provided, each container
has a first wall portion and a second wall portion arranged to face each
other, in each container, the second transparent material is arranged
around the first wall portion, and the first wall portions of the two
containers are bonded to each other.

[0020] According to the invention, in each of the two containers, the
interface is formed in a shape rounded from the first wall portion toward
the second wall portion, and the first wall portions of the two
containers are bonded to each other. With this configuration, a convex
lens can be formed over the two containers such that the bonded first
wall portions are included in a cross-section.

[0021] According to an optical element array in which a plurality of
optical elements are arranged, in each optical element, it is possible to
control the shape of the interface formed in the container. Thus, it is
possible to freely change the refractive power of each optical element.
For example, if a plurality of light sources are arranged and the optical
elements are arranged to correspond to the light sources, it is possible
to freely condense or diffuse light emitted from a plurality of light
sources.

[0022] The invention provides a method of manufacturing an optical element
in which a conductive liquid is filled in a container transmitting light.
The method includes an electrode forming step of using a container having
one opened surface, forming a first electrode at a position of the one
surface, and forming a second electrode at a position of another surface
facing the one surface, a liquid inflow step of charging a liquid,
applying a voltage having reverse charge to the liquid to the first
electrode, and allowing the liquid to flow into the container from the
one surface, and a liquid filling step of applying a voltage having the
same charge as the liquid to the first electrode, applying a voltage
having reverse charge to the liquid to the second electrode, and filling
the liquid in the container.

[0023] In the method of manufacturing an optical element according to the
invention, in the liquid inflow step, the charged liquid flows into the
container from the one surface, and a voltage having reverse charge to
the liquid is applied to the first electrode formed at the position of
the one surface. For this reason, the wetness of the liquid in contact
with the surface of the first electrode is improved. Thus, it is possible
to allow the liquid to smoothly flow from the one surface. In the liquid
filling step, a voltage having the same charge as the liquid is applied
to the first electrode, and a voltage having reverse charge to the liquid
is applied to the second electrode. For this reason, the wetness of the
liquid in contact with the surface of the second electrode is improved.
Thus, it is possible to fill the liquid at the corners in the periphery
of another surface.

[0024] According to the method of manufacturing an optical element, even
when the container is of a small size, the liquid can be filled at the
corners of the container. Therefore, it is possible to appropriately
manufacture the optical element and the optical element array in which
the transparent material is accommodated in the container.

Advantageous Effects of Invention

[0025] According to the invention, it is possible to reduce a voltage to
be applied and also to form a desired interface shape.

BRIEF DESCRIPTION OF DRAWINGS

[0026] FIG. 1 is an outline diagram showing an optical element according
to a first embodiment of the invention.

[0027]FIG. 2 is a sectional view of a container part taken along the line
II-II of FIG. 1.

[0028]FIG. 3 is a conceptual diagram showing the growing state of bubbles
in the optical element of FIG. 1.

[0029]FIG. 4 is a sectional view of a container part taken along the line
IV-IV of FIG. 3.

[0030]FIG. 5 is a sectional side view showing a relationship between
curvature and refractive power of a lens.

[0031]FIG. 6 is an outline diagram showing an optical element array in
which a plurality of optical elements of FIG. 1 are arranged.

[0033]FIG. 8 is a diagram showing an example of an optical system using
the optical element array of FIG. 6.

[0034]FIG. 9 is a sectional view and a top view showing a manufacturing
process of the optical element array of FIG. 6.

[0035] FIG. 10 is a sectional view and a top view showing a manufacturing
process subsequent to FIG. 9.

[0036]FIG. 11 is a sectional view and a top view showing a manufacturing
process subsequent to FIG. 10.

[0037] FIG. 12 is a sectional view and a top view showing a manufacturing
process subsequent to FIG. 11.

[0038]FIG. 13 is a sectional view and a top view showing a manufacturing
process subsequent to FIG. 12.

[0039] FIG. 14 is a sectional side view of a container part in an optical
element according to a second embodiment.

[0040] FIG. 15 is a sectional side view of a container part in an optical
element according to a third embodiment.

[0041] FIG. 16 is a sectional side view of a container part in an optical
element according to a fourth embodiment.

[0042]FIG. 17 is a diagram showing a video display example when the
optical element of FIG. 16 is applied to a head-up display.

[0043] FIG. 18 is a side sectional view of a container part in an optical
element according to a fifth embodiment.

[0044] FIG. 19 is a side view of an optical element array in which a
plurality of optical elements shown in FIG. 18 are arranged.

DESCRIPTION OF EMBODIMENTS

[0045] Hereinafter, an optical element according to an embodiment of the
invention will be described with reference to the drawings. In the
description of the drawings, the same elements are represented by the
same reference numbers, and overlapping description will be omitted.

First Embodiment

[0046] FIG. 1 is an outline diagram showing an optical element according
to a first embodiment. FIG. 2 is a sectional view of a container part
taken along the line II-II of FIG. 1. A microlens (optical element) 1 of
this embodiment is arranged on the emission side of, for example, a laser
light source, and refracts laser light emitted from the laser light
source.

[0047] The microlens 1 includes a hollow container 10 which substantially
has a cubic shape and transmits light. The container 10 is formed of a
transparent insulating film, and is constituted by a six-face wall
portion 11 having a predetermined thickness. The six-face wall portion 11
forms an internal space S substantially having a closed cubic shape, and
the container 10 is configured such that a liquid or gas can be filled in
the internal space S. Examples of the transparent insulating film forming
the container 10 include strontium titanate, lithium niobate, and the
like. The size of the container 10 is not particularly limited, and the
length of one side is typically about 50 to 100 μm.

[0048] In the six-face wall portion 11 constituting the container 10, a
first sidewall (wall portion) 11a and a second sidewall (wall portion)
11b (see FIG. 2) which are wall portions arranged to face each other
function as the light-transmissive surface of the container 10. Although
in FIG. 1, to facilitate understanding of the internal configuration of
the container 10, the first sidewall 11a is not shown, and the first
sidewall 11a is located in the near-side face of the drawing.
Hereinafter, the first sidewall 11a and the second sidewall 11b are also
simply referred to as "sidewalls 11a and 11b".

[0049] In addition to the container 10, the microlens 1 includes
plate-shaped heaters (heat-generating portion) 12 and 12 which are
respectively formed in the sidewalls 11 and 11b to generate heat through
electrical connection, a control part 3 which is connected to the heaters
12 and 12 by wirings 4 to apply a current to the heaters 12 and 12 and to
control the amount of heat generation, and plate-shaped insulating films
13 and 13 which are formed so as to cover the surfaces (the surfaces on
the internal space S side) 12a of the heaters 12 and 12 from the internal
space S side of the container 10. In FIG. 2, the control part 3 is not
shown (hereinafter, the same is applied to FIGS. 4, 5, 7, and 8).

[0050] The microlens 1 includes a transparent liquid (first transparent
material) 16 which is accommodated in the container 10 and forms a liquid
phase (first phase), and microbubbles (second transparent material) 17
which are bubbles accommodated in the container 10 to form a gas phase
(second phase), an interface B (see FIG. 2) on a curve rounded toward the
transparent liquid 16 being formed between the transparent liquid 16 and
the microbubbles 17. That is, the transparent liquid 16 and the
microbubbles 17 form different phases.

[0051] The heaters 12 generate heat and transmit heat to the microbubbles
17 and the transparent liquid 16, such that the microbubbles 17 and the
transparent liquid 16 thermally expand or contract. The heater 12 is a
transparent electrode which is formed of zinc oxide (ZnO), indium tin
oxide (ITO), or the like. The heaters 12 are formed in a part on the
inner wall surfaces of the sidewalls 11a and 11b. The heaters 12 extend
over an upper wall 11c and a lower wall 11d (hereinafter, also simply
referred to as "walls 11c and 11d") which connect the end sides of the
sidewalls 11a and 11b and face each other. That is, the heaters 12 are
configured such that the length thereof in the longitudinal direction
(the up-down direction of FIG. 1) is slightly longer than the length of
one side of the internal space S, and the end portions 12c and 12d in the
longitudinal direction are respectively in contact with the walls 11c and
11d.

[0052] In the following description, the direction perpendicular to the
wall surfaces of the sidewalls 11a and 11b (the direction perpendicular
to the heaters 12) is referred to as the "thickness direction", the
direction perpendicular to the walls 11c and 11d (the direction parallel
to the longitudinal direction of the heaters 12) is referred to as the
"length direction", and the direction parallel to the sidewalls 11a and
11b and the walls 11c and 11d (the direction parallel to the lateral
direction of the heaters 12) is referred to as the "width direction".

[0053] As shown in FIG. 1, the end portions 12c and 12d of the heaters 12
have a length in the width direction corresponding to a width L1. Each
heater 12 has a small-width portion 12e at the center thereof. Here, the
term "center" refers to the intermediate position between one end portion
12c and another end portion 12d, and includes "substantially center". The
small-width portion 12e has a length in the width direction which
corresponds to a width L2 smaller than the width L1. The heater 12 has a
shape with a gradually decreasing length in the width direction from the
end portions 12c and 12d toward the small-width portion 12e. In this way,
the heater 12 has a shape symmetrical with respect to the small-width
portion 12e.

[0054] The control part 3 controls the amount of heat generation of the
heaters 12 to thermally expand or contract the microbubbles 17 and the
transparent liquid 16, and controls the curvature of the interface B. In
other words, the control part 3 carries out temperature adjustment of the
microbubbles 17 and the transparent liquid 16 to control the shape of the
interface B. The control part 3 has means for detecting the amount of
heat generation of the heaters 12 or the temperature of the microbubbles
17 and the transparent liquid 16. The control part 3 performs control to
supply the transparent liquid 16 into the container 10 and control to
discharge the transparent liquid 16 from the container 10. In the control
to supply and discharge the transparent liquid 16, any method may be used
insofar as the transparent liquid 16 can be supplied and discharged
through the container 10. The control part 3 has a computer which
includes a CPU (Central Processing Unit), a ROM (Read Only Memory), and a
RAM (Random Access Memory) for an arithmetic operation relating to shape
control of the interface B.

[0055] The insulating films 13 covering the heaters 12 prevent the heaters
12 from coming into contact with the microbubbles 17 and the transparent
liquid 16 and transmit heat from the heaters 12 to the microbubbles 17
and the transparent liquid 16. The insulating films 13 are formed of a
transparent insulating film, such as strontium titanate or lithium
niobate, and covers the entire surfaces 12a of the heaters 12.
Specifically, each insulating film 13 has an outer shape slightly greater
than the outer shape of the heater 12. That is, the end portions 13c and
13d of the insulating film 13 in the length direction have a length
slightly longer than the width L1 of the end portions 12c and 12d of the
heater 12. The insulating film 13 covers the end surface (not shown)
extending in the thickness direction in the end portion 12f (see FIG. 1)
of the heater 12 in the width direction. The wirings 4 are respectively
connected to the end portions 12c and 12d.

[0056] Here, in each of the first sidewall 11a, the second sidewall 11b,
and the insulating film 13, it is preferable that the surface facing the
internal space S is processed so as to improve wetness for shape control
of the microbubbles 17 described below.

[0057] The container 10, the heaters 12, the control part 3, the wirings
4, and the insulating films 13 can be manufactured by an existing
semiconductor manufacturing technique. The manufacturing method is the
same as a manufacturing processing of a microlens array described below.

[0058] The transparent liquid 16 and the microbubbles 17 have different
phases, and are materials having the same composition. As the transparent
liquid 16 and the microbubbles 17, for example, perfluorocarbon
(Fluorinert (Registered Trademark)), silicone, or the like may be used.
The transparent liquid 16 locally boils when receiving heat from the
heater 12, and becomes vapor bubbles, which become the microbubbles 17.
At this time, the transparent liquid 16 is discharged by the control part
3 such that the total volume of the transparent liquid 16 and the
microbubbles 17 coincides with the volume of the internal space S. The
microbubbles 17 are cooled through heat release from the container 10 to
the outside and condensed to become the transparent liquid 16. At this
time, the transparent liquid 16 is supplied by the control part 3 such
that the total volume of the transparent liquid 16 and the microbubbles
17 coincides with the volume of the internal space S. With this control,
the total volume of the transparent liquid 16 and the microbubbles 17
coincides with the volume of the internal space S. The transparent liquid
16 and the microbubbles 17 are controlled to have predetermined volume
and shape by the control part 3.

[0059] The microbubbles 17 are symmetrically arranged separately at two
places around the first sidewall 11a and the second sidewall 11b (see
FIG. 2). The microbubbles 17 substantially have a dome shape rounded so
as to approach each other, and the bottom surfaces 18 thereof come into
contact with the sidewalls 11a and 11b and the insulating film 13 and are
inscribed in the internal space S when viewed from the thickness
direction (see FIG. 1). The microbubbles 17 have a spherical shape
(curved shape) in which the dome portions 19 (see FIG. 2) thereof are
rounded inside the internal space S, and the interface B is formed
between the transparent liquid 16 and the microbubbles 17. A contact
angle between the rising portions of the dome portions 19 (the portions
near the bottom surface 18) and the sidewalls 11a and 11b is determined
at a predetermined angle θ depending on the state of surface
treatment.

[0060] In the following description, the microbubble 17 formed around the
first sidewall 11a is referred to as an incidence-side microbubble 17a,
and the microbubble 17 formed around the second sidewall 11b is referred
to as an emission-side microbubble 17b (see FIG. 2).

[0061] The incidence-side microbubble 17a and the emission-side
microbubble 17b are separated at a distance d in the thickness direction.
The transparent liquid 16 is arranged so as to be sandwiched from both
sides thereof by the incidence-side microbubble 17a and the emission-side
microbubble 17b. The interface B is formed which has two faces between
the incidence-side microbubble 17a and the transparent liquid 16 and
between the emission-side microbubble 17b and the transparent liquid 16,
such that a concave lens is formed between the first sidewall 11a and the
second sidewall 11b.

[0062] The incidence-side microbubble 17a and the emission-side
microbubble 17b may not be symmetrically arranged and may have different
shapes. Shape control of the microbubble 17 will be described below.

[0063]FIG. 3 is a conceptual diagram showing the growing state of a
bubble in the microlens 1. FIG. 4 is a sectional view of a container 10
part taken along the line Iv-Iv of FIG. 3. First, the transparent liquid
16 at a predetermined temperature is filled in the container 10. If a
voltage is applied to the heaters 12 by the control part 3 and a current
flows in the heaters 12, the small-width portions 12e of the heaters 12
generate heat in accordance with the following expression (1).

[Equation 1]

Q=RI2=mct (1)

[0064] In the expression (1), the following definition is made.

Q: an amount of heat generation R: resistance of the small-width portion
12e I: current flowing in the heater 12 m: the weight of the transparent
liquid 16 c: specific heat of the transparent liquid 16 t: an electrical
connection time

[0065] If heat is generated in the small-width portion 12e of each heater
12 with the amount Q of heat generation, heat is transmitted to the
transparent liquid 16 through the insulating film 13, and the transparent
liquid 16 is locally vaporized at the position corresponding to the
small-width portion 12e. An initial microbubble 17 is generated around
the small-width portion 12e (see a virtual line in FIGS. 3 and 4). The
microbubble 17 increases in size with the elapse of the electrical
connection time t.

[0066] Here, if the following definition is made, the relationship of the
following expression (2) is established.

r: the radius of the dome portion 19 of the microbubble 17 K: the
curvature of the interface B

[ Equation 2 ] r = 1 K ( 2 )
##EQU00001##

[0067] The container 10 of the microlens 1 constantly exchanges heat with
the outside and is deprived of a predetermined amount Qout of heat.
Thus, if electrical connection is stopped after the initial microbubble
17 is generated, the radius r of the microbubble 17 decreases such that
an internal pressure P is equal to the surface tension of the transparent
liquid 16. The amount Qout of heat emitted from the container 10 is
influenced by the coefficient of heat conduction of the wall portion 11
of the container 10.

[0068] The transparent liquid 16 deprived of heat decreases in
temperature, and the microbubble 17 is also deprived of heat through the
interface B. As a result, the temperature decreases by a temperature
change ΔT. The proportional relationship of the following
expression (3) is established between the amount Qout of heat and
the temperature change ΔT.

[Equation 3]

ΔQ0∞ΔT (3)

[0069] The following expression (4) is established by the equation of
state of gas. For this reason, if the temperature decreases by the
temperature change ΔT, the product of the internal pressure PB
of the microbubble 17 and a volume change ΔV decreases.

[Equation 4]

PBΔV=nRΔT (4)

[0070] Here, the following definition is made.

PB: an internal pressure of the microbubble 17 ΔV: a volume
change of the microbubble 17 n: the number of moles of the microbubble 17
R: a gas constant ΔT: a temperature change of the microbubble 17

[0071] As the product PBΔV of the internal pressure PB and
the volume change ΔV decreases, the internal pressure PB
becomes equal to an external pressure when the microbubble 17 is pressed
from the transparent liquid 16. For this reason, the volume of the
microbubble 17 decreases until the internal pressure PB becomes
equal to the external pressure.

[0072] In order to maintain the radius r of the microbubble 17, it is
necessary to continuously give a predetermined amount Qe of heat by the
heater 12. The radius r of the microbubble 17 can expand or contract by
turning on or off the heater 12 to selectively give a predetermined
amount Qe of heat. The relationship between the amount Q of heat
generation of the heater 12 and the radius r of the microbubble 17 is as
expressed by the following expression (5).

[0073] Thus, it is possible to control the shape and the radius r (that
is, the curvature K) of the microbubble 17 (interface B) by turning on or
off of the heater 12, thereby controlling the refractive power of the
above-described concave lens.

[0074] As described above, in the microlens 1 of this embodiment, the
heaters 12, the control part 3, the wirings 4, and the insulating films
13 are provided to constitute a curvature control part (interface shape
control means) 6 which controls the shape of the interface B. That is,
the curvature control part 6 has a function of carrying out temperature
adjustment of the transparent liquid 16 and the microbubbles 17 to
thermally expand or contract the transparent liquid 16 and the
microbubbles 17, and controlling the curvature K of the interface B by
thermal expansion or contraction.

[0075]FIG. 5 is a sectional side view showing a relationship between
curvature and refractive power of a lens. As shown in FIG. 5(a), when the
incidence-side microbubble 17a and the emission-side microbubble 17b are
separated at the distance d, the refractive power (lens power) φ is
expressed by the following expression (6).

φ: refractive power (lens power) of the microlens 1 na: a
refractive index of the transparent liquid 16 K1: curvature of the
interface B formed by the incidence-side microbubble 17a K2:
curvature of the interface B formed by the emission-side microbubble 17b
d: the distance between the incidence-side microbubble 17a and the
emission-side microbubble 17b

[0077] As expressed by the above-described expression (2), if the radii of
the incidence-side microbubble 17a and the emission-side microbubble 17b
are determined, the curvatures K1 and K2 are determined. As
expressed by the expression (6), predetermined refractive power φ is
obtained for predetermined curvatures K1 and K2.

[0078] For example, as shown in FIG. 5(b), if the curvatures K1 and
K2 become greater than those shown in FIG. 5(a), the refractive
power φ increases, and the refractive effect of light by the
microlens 1 is intensified. As shown in FIG. 5(c), if the curvatures
K1 and K2 become smaller than those shown in FIG. 5(a), the
refractive power φ decreases, and the refractive effect of light by
the microlens 1 is weakened.

[0079] Next, microlens array of this embodiment in which a plurality of
microlenses 1 are arranged will be described. FIG. 6 is an outline
diagram showing a microlens array in which a plurality of microlenses 1
of FIG. 1 are arranged. FIG. 7 is a side view of a container part in FIG.
6. As shown in FIGS. 6 and 7, a microlens array (optical element array)
30 is configured such that a plurality of microlenses 1 are arranged in
the length direction and the width direction. In the microlens array 30,
the microlenses 1 are arranged in a matrix of M rows and N columns (where
M and N are natural numbers). The microlens array 30 includes containers
10 which are arranged in a matrix of M rows and N columns, and a control
part 33 which is connected to the containers 10 through wirings 4 and
controls the amount of heat generation of the heater 12 in each container
10.

[0080] In the microlens array 30, the control part 33, the wirings 4, the
heater 12 of each microlens 1, and the insulating films 13 (see FIG. 1)
are provided to constitute a curvature control part (interface shape
control means) 36 which controls the shape of the interface B. The
control part 33 may include the control part 3 (see FIG. 1) of the
microlens 1 for each microlens 1, or may be collectively constituted as a
single device to control the shape of the interface B in each container
10.

[0081] In the microlens array 30, the curvature K of the interface B
formed in each container 10 is controlled, making it possible to freely
change the refractive power φ of each microlens 1. For example, in
the microlens array 30, the refractive power φj in a j-th column
becomes refractive power φ1,j to φ.sub.M,j, and the
refractive power in the microlens 1 of the i-th row and the j-th column
becomes refractive power φi,j (see FIG. 7).

[0082] As shown in FIG. 8, an optical system 100 using a microlens array
can be constituted. The optical system 100 has a plurality of light
sources (for example, laser light sources or the like) 35, and a
microlens array 30A in which microlenses 1 are arranged to correspond to
the light sources 35. The optical system 100 also has an optical relay
lens 37 which is arranged between the microlens array 30A and a
projection surface 36. In the optical system 100, it becomes possible to
carry out enlargement or reduction of a projected image on the projection
surface 36, fluctuation correction, or the like.

[0083] Subsequently, a method of manufacturing the microlens array 30 will
be described. FIGS. 9 to 13 are sectional views and top views of a
manufacturing process of the microlens array 30 of FIG. 6. In the
respective drawings, the left side is a sectional view when viewed from
the length direction, and the right side is a top view when viewed from
the thickness direction. In the sectional view, an example is shown where
the number of microlenses is 4. In the top view, only one microlens 1 is
shown. In the following description, a case will be described where
lithium niobate is used for the container 10, and an ITO electrode is
used for the heater 12.

[0084] First, as shown in FIG. 9(a), a lithium niobate substrate 50 having
a predetermined thickness is prepared (S1). Next, as shown in FIG. 9(b),
voids 51 having a substantially cubic shape are formed such that one
surface in the thickness direction is opened by etching (S2). Here, each
void 51 correspond to the internal space S of the container 10. The
opened surface of each void 51 is referred to as a top surface (one
surface) 51a, and a surface facing the one surface is referred to as a
bottom surface (another surface) 51b.

[0085] Next, as shown in FIG. 10(a), a lower ITO electrode 52 is formed at
the position of the bottom surface 51b of each void 51 (S3). The lower
ITO electrode 52 corresponds to the heater 12. Next, as shown in FIG.
10(b), an oxide film 53 is deposited at a predetermined height in each
void 51 directly below the position of the top surface 51a (S4).

[0086] Next, as shown in FIG. 11(a), an upper ITO electrode 54 is formed
at the position of the top surface 51a (S5). The upper ITO electrode 54
corresponds to the heater 12. Next, as shown in FIG. 11(b), the oxide
film 53 is removed by etching (S6). That is, Steps S3 to S6 correspond to
an electrode forming step of using a lithium niobate substrate
(container) 50 having the opened top surface 51a, forming the upper ITO
electrode (first electrode) 54 at the position of the top surface 51a,
and forming the lower ITO electrode (second electrode) 52 at the position
of the bottom surface 51b. The wiring 4 which connects the heater 12 and
the control part 33 is formed in the same manner as the heater 12.

[0087] Next, as shown in FIG. 12(a), a gate oxide film 56 is formed so as
to cover the lower ITO electrode 52 and the upper ITO electrode 54 (S7).
The gate oxide film 56 corresponds to the insulating film 13. The gate
oxide film 56 can be formed by a known CVD (Chemical Vapor Deposition)
method in the related art.

[0088] Next, as shown in FIG. 12(b), a conductive liquid filler 57, such
as perfluorocarbon, is prepared, and a positive voltage is applied to the
filler 57 (the filler 57 is positively charged). The side (the lower side
in the drawing) of the upper ITO electrode 54 facing the void 51 is
connected to GND (grounded). The filler 57 flows from the top surface 51a
into the void 51 (S8). The filler 57 corresponds to the transparent
liquid 16. That is, Step S8 corresponds to a liquid inflow step of
charging the filler 57, applying a voltage having reverse charge to the
filler 57 to the upper ITO electrode 54, and allowing the filler 57 to
flow from the top surface 51a into the container. According to the liquid
inflow method, a so-called electrowetting phenomenon occurs to improve
wetness of the filler 57 with respect to the upper ITO electrode 54 and
to promote the inflow of the filler 57.

[0089] Next, as shown in FIG. 13(a), a positive voltage is applied to the
lower ITO electrode 52. The upper ITO electrode 54 is connected to GND
(grounded). The filler 57 is filled in the void 51 (S9). That is, Step S9
corresponds to a liquid filling step of applying a voltage having the
same charge as the filler 57 to the upper ITO electrode 54, applying a
voltage having reverse charge to the filler 57 to the lower ITO electrode
52, and filling the filler 57 in the container. According to the liquid
filling method, a so-called electrowetting phenomenon occurs to improve
wetness of the filler 57 with respect to the lower ITO electrode 52, such
that the filler 57 is filled around the lower ITO electrode 52 with no
gap.

[0090] As shown in FIG. 13(b), UV curable resin 58 is formed so as to
cover the top surface 51a of each of a plurality of voids 51 in the width
direction and the length direction, and the voids 51 are sealed (S10).
That is, through Step S10, the filler 57 is filled in the voids 51.
Though not shown, the control part 33 (see FIG. 6) is connected to the
lower ITO electrode 52 and the upper ITO electrode 54 through the wirings
4.

[0091] Through the sequence of steps, the microlens array 30 shown in FIG.
6 is manufactured.

[0092] According to the microlens 1 and the microlens array 30 of this
embodiment, the transparent liquid 16 forming a liquid phase and the
microbubbles 17 forming a gas phase are subjected to temperature
adjustment by the curvature control part 6. The transparent liquid 16 and
the microbubbles 17 subjected to temperature adjustment thermally expand
or contract, such that the curved interface B formed between the
transparent liquid 16 and the microbubbles 17 is changed. Thus, it
becomes possible to control the interface shape, thereby forming a
desired interface shape. Since Joule heat based on current application is
used for temperature adjustment, it is possible to reduce a voltage to be
applied compared to a case where a voltage is directly applied to the
transparent liquid 16 or the microbubbles 17 in the container 10 to
change the surface tension of the transparent liquid 16 or the
microbubbles 17. Therefore, according to the microlens 1 and the
microlens array 30, it is possible to reduce a voltage to be applied and
also to form a desired interface shape.

[0093] For example, in an electrowetting method of the related art in
which a voltage is directly applied, it is necessary to apply a voltage
of about 100 V. In contrast, in this embodiment, it is possible to
control the shape of the interface B with a very low voltage of about 5
V.

[0094] According to the microlens 1 and the microlens array 30, the
microbubbles 17 forming a gas phase is hardly influenced by gravity
because of a small mass per volume (low density). Therefore, it is
possible to control the shape of the interface B accurately.

[0095] According to the microlens 1 and the microlens array 30, the
transparent liquid 16 and the microbubbles 17 thermally expand or
contract by the curvature control part 6, making it easy to change the
shape of the interface B. Therefore, it becomes possible to control the
interface shape.

[0096] According to the microlens 1 and the microlens array 30, since the
curvature of the interface B is controlled by the curvature control part
6, it is possible to control refractive power φ when light passes
through the container 10.

[0097] According to the microlens 1 and the microlens array 30, since
electrical resistance increases in the small-width portion 12e at the
center of the heater 12, the temperature of the small-width portion 12e
is at the highest in the heater 12. Thus, it is possible to sufficiently
heat the transparent liquid 16 or the microbubbles 17 near the center of
the heater 12 with a small current. Therefore, it is possible to easily
thermally expand the transparent liquid 16 or the microbubbles 17 and to
easily change the phase of the transparent liquid 16 or the microbubbles
17, making it easy to control the shape of the transparent liquid 16 or
the microbubbles 17.

[0098] According to the microlens 1 and the microlens array 30, the
transparent liquid 16 is arranged so as to be sandwiched from both sides
thereof by the incidence-side microbubble 17a and the emission-side
microbubble 17b between the first sidewall 11a and the second sidewall
11b. For this reason, the interface B is formed which has two faces
respectively rounded from the first sidewall 11a and the second sidewall
11b inside the container 10. Therefore, a concave lens can be formed
between the first sidewall 11a and the second sidewall 11b by the
two-face interface B.

[0099] According to the microlens 1 and the microlens array 30, it is
possible to easily control the radius r of the microbubbles 17 depending
on the electrical connection time t to the heaters 12 or the magnitude of
a current I to be applied, thereby changing the refractive power φ of
the lens. Since the refractive power φ depends on only the radius r
of the dome portions 19 of the microbubbles 17, even when the liquid
quality of the transparent liquid 16 is changed, it is possible to easily
correct the refractive power φ only by changing the current I to be
applied.

[0100] According to the microlens 1 and the microlens array 30, since the
interface B is formed by a liquid phase and a gas phase, unlike the
liquid phases, there is no case where the phases are mixed. Thus, it is
possible to easily form the interface B and there is little change in the
quality of the material. As described above, since the gas phase is
hardly influenced by gravity, as the container 10 decreases in size, the
container 10 is robust to gravity. The size or shape of the microbubbles
17 is determined by balance of heat release outside the container 10 and
heating by the heaters 12, thereby easily controlling the shape of the
interface B.

[0101] According to the microlens array 30, in each microlens 1, it is
possible to control the shape of the interface B formed in the container
10. Therefore, it is possible to freely change the refractive power of
each microlens 1. For example, if a plurality of light sources 35 are
arranged and the microlenses 1 are arranged to correspond to the light
sources 35, it is possible to freely condense or diffuse light emitted
from a plurality of light sources 35.

[0102] According to the method of manufacturing the microlens array 30 of
this embodiment, in the liquid inflow step S8, when the charged filler 57
flows into the void 51 from the top surface 51a, a voltage having reverse
charge to the filler 57 is applied to the upper ITO electrode 54 formed
in the top surface 51a. For this reason, wetness of the filler 57 in
contact with the surface of the upper ITO electrode 54 is improved.
Therefore, it is possible to achieve a smooth inflow of the filler 57
from the top surface 51a. In the liquid filling step S9, a voltage having
the same charge as the filler 57 is applied to the upper ITO electrode
54, and a voltage having reverse charge to the filler 57 is applied to
the lower ITO electrode 52. For this reason, wetness of the filler 57 in
contact with the surface of the lower ITO electrode 52 is improved.
Therefore, it is possible to fill the filler 57 at the corners in the
periphery of the bottom surface 51b.

[0103] According to the method of manufacturing an optical element, even
when the container 10 is small, it is possible to fill the filler 57 at
the corners of the container 10. Therefore, it is possible to
appropriately manufacture the microlens 1 and the microlens array 30.

Second Embodiment

[0104] FIG. 14 is a sectional side view of a container part in a microlens
according to a second embodiment. As shown in FIG. 14, a microlens 1A of
this embodiment is different in the microlens 1 of the first embodiment
shown in FIGS. 1 and 2 in that heaters 12A serving as a heat-generating
portion are provided in an upper wall 11c and a lower wall 11d. The
heaters 12A are formed on the inner wall surfaces of the upper wall 11c
and the lower wall 11d, and extend in the thickness direction from around
the second sidewall 11b to near the centers of the walls 11c and 11d.
Insulating films 13A are formed so as to cover the heaters 12A. In FIG.
14, the control part 3 is not shown (hereinafter, the same is applied to
FIGS. 15, 16, 18, and 19).

[0105] According to the microlens 1A, the incidence-side microbubble 17a
and the emission-side microbubble 17b can be asymmetrically shaped.
Specifically, the emission-side microbubble 17b can be arranged in the
periphery of the second sidewall 11b as well as in the periphery of the
walls 11c and 11d, and the radius r can be increased. With this
configuration, it is possible to increase the curvature of the
incidence-side microbubble 17a and also to control the curvature of the
emission-side microbubble 17b.

Third Embodiment

[0106] FIG. 15 is a sectional side view of a container part in a microlens
according to a third embodiment. As shown in FIG. 15, a microlens 1B of
this embodiment is different from the microlens 1 of the first embodiment
shown in FIGS. 1 and 2 in that Peltier elements 20 serving as a cooling
section are buried in an upper wall 11c and a lower wall 11d. The Peltier
elements 20 may be substantially buried over the entire surfaces of the
upper wall 11c and the lower wall 11d or may be buried in a part of the
upper wall 11c and the lower wall 11d.

[0107] According to the microlens 1B, it is possible to efficiently cool
the microbubbles 17 in the container 10 by the Peltier elements 20 and to
increase a response speed in the course of heat absorption. Thus, it is
possible to improve response performance at the time of switching between
heat generation and heat absorption and to rapidly control the size of
the microbubbles 17. In this embodiment, a route in which heat absorption
occurs is in order of the microbubbles 17, the transparent liquid 16, the
walls 11c and 11d, and the Peltier elements 20.

Fourth Embodiment

[0108] FIG. 16 is a sectional side view of a container part in a microlens
according to a fourth embodiment. As shown in FIG. 16, a microlens 1C of
this embodiment is different from the microlens 1B of the third
embodiment shown in FIG. 15 in that heaters 22a to 22i and heaters 23a to
23i serving as a plurality of small heat-generating portions arranged to
be separated from each other in the thickness direction are provided in
an upper wall 11c and a lower wall 11d. The heaters 22a to 22i and the
heaters 23a to 23i may be substantially formed over the entire surfaces
of the upper wall 11c and the lower wall 11d or may be formed in a part
of the upper wall 11c and the lower wall 11d. Insulating films 13C are
formed so as to cover the heaters 22a to 22i and the heaters 23a to 23i.

[0109] According to the microlens 1C, it is possible to finely control the
wet state by the transparent liquid 16 (or the generation state of the
microbubbles 17) in the upper wall 11c and the lower wall 11d by the
heaters 22a to 22i and the heaters 23a to 23i. In the example shown in
FIG. 16, some heaters 22f to 22i on the upper wall 11c side and all the
heaters 23a to 23i on the lower wall 11d side are turned on, such that
wetness of the wall surfaces of the insulating films 13C near the heaters
is improved and the occurrence of microbubbles 17C is advanced, thereby
forming the interface B shown in FIG. 16. Therefore, it becomes possible
to control the emission angle of light.

[0110] In the microlens 1C, the emission angle of light can be controlled
in the above-described manner. For this reason, when a plurality of
microlenses 1C are arranged to constitute the same system as the optical
system 100 shown in FIG. 8, it is possible to make a focal distance
variable. When the system is applied to a head-up display (HUD) for a
vehicle, it is possible to use both a distant display image and a near
display image in HUD display.

[0111] For example, in a normal display state shown in FIG. 17(a), "75
km/h" representing a vehicle speed is displayed at a predetermined
position in front of a driver. Meanwhile, in a display state in an
emergency, such as display of a warning (warning information), as shown
in FIG. 17(b), a message in an emergency "engine abnormality" is
displayed so as to be viewed near the driver. In this way, in an
emergency, warning information is displayed as a near display image, such
that the driver can instantaneously notice the warning information.

Fifth Embodiment

[0112] FIG. 18 is a sectional side view of a container part in a microlens
according to a fifth embodiment. As shown in FIG. 18, a microlens 1D of
this embodiment is different from the microlens 1 of the first embodiment
shown in FIGS. 1 and 2 in that two containers 10 are provided, the first
sidewalls 11a of the container 10 are bonded to each other, microbubbles
17D are arranged only around the first sidewalls 11a, and no microbubble
is arranged around the second sidewalls 11b.

[0113] Specifically, in the microlens 1D, the heaters 12 formed on the
first sidewall 11a side is turned on, and the heaters 12 formed on the
second sidewall 11b side is turned off. When this happens, the
microbubbles 17D can be generated only around the first sidewalls 11a.

[0114] According to the microlens 1D, a convex lens can be formed over the
two containers 10 such that the bonded first sidewalls 11a are included
in the cross-section. The microlenses 1D may be arranged in the length
direction to constitute a convex lens array 80 shown in FIG. 19.

[0115] Although the embodiments of the invention have been described, the
invention is not limited to the foregoing embodiments. For example,
although in the foregoing embodiments, a case has been described where
all the wall portions of the six faces of the container 10 are formed of
a transparent insulating film, only the sidewalls 11a and 11b may be
formed of a transparent insulating film. That is, the four faces
excluding the sidewalls 11a and 11b may be formed of a nontransparent
insulating film.

[0116] Although in the foregoing embodiments, a case has been described
where the transparent liquid 16 and the microbubbles 17 are subjected to
temperature adjustment by the curvature control part 6, either the
transparent liquid 16 or the microbubbles 17 may be subjected to
temperature adjustment by the curvature control part 6.

INDUSTRIAL APPLICABILITY

[0117] According to the invention, it is possible to reduce a voltage to
be applied and also to form a desired interface shape.